Electromagnetic trip and installation switching devices of the kind mentioned above are usually electro-mechanical devices. The point of contact includes a fixed contact member and a movable contact member which is held by a movable contact arm or contact bridge. In the closed position, the movable contact member is pressed against the fixed contact member influenced by the force of a contact spring.
Such trip devices and installation switching devices can also include a mechanical gear mechanism with a latch and a spring force based energy storage assembly.
In case of a tripping condition, a tripping device is known to act on the latch, which then releases the energy from the energy storage so that the gear mechanism can act upon the contact lever or contact bridge in order to open the point of contact. Known tripping devices, are for example, thermal tripping devices based on bimetal or thermal shape memory alloys, short circuit tripping devices based on a fast moving electromagnetic armature, and residual current tripping devices based on an integrating current transformer coupled to an electromagnetic armature.
An electromagnetic trip device for a circuit breaker is described, for example, in WO 2006 117 097 A2. The trip device has a yoke, a coil, a magnetic core and a magnetic armature, where the armature is coupled to a pin jutting out from the device in case of a short circuit current. When jutting out, the pin acts on a movable contact lever for directly opening a contact point. Due to the various mechanical pieces involved, each having a non-neglectable mechanical inertia, the delay time between occurrence of the short circuit current and the opening of the contact point cannot fall below a lower limit in the range of several milliseconds.
The known mechanical setup of trip devices and of the kind mentioned leads to limitations when it comes to tripping and switching speed, due to the inertia of the masses of the levers and other gear components involved.
In a range of low voltage applications, known electromechanical actuators are too slow. For example, breakers in low voltage systems (e.g., power supply for telecom) need to be fast operating in order to provide selectivity and protection, faster than is today possible with the known electro-mechanical devices. As a result, presently the only alternative is an electronic switch. This, however, has the disadvantage of missing galvanic separation, which can only be achieved in mechanically operating circuit breakers.